Aircraft rotor blade and blade flap pitch control



Jan. 8, 1952 E. A. STALKER 2,581,773

AIRCRAFT ROTOR BLADE AND BLADE FLAP PITCH CONTROL Filed Nov. 2, 1945 4 Sheets-Sheet 1 FIG. 5

I N VEN TOR.

Jan. 8, 1952 E. A. STALKER 2,581,773

AIRCRAFT ROTOR BLADE AND BLADE FLAP PITCH CONTROL Filed Nov. 2, 1945 4 Sheets-Sheet 2 o Fl G. 8 I A Q I N VEN TOR.

Jan. 8, 1952 E. A. STALKER 2,581,773

AIRCRAFT ROTOR BLADE AND BLADE FLAP PITCH CONTROL Filed Nov. 2, 1945 4 Sheets-Sheet 3 IN VEN TOR.

Jan. 8, 1952 E. A. STALKER 7 AIRCRAFT ROTOR BLADE AND BLADE FLAP PITCH CQNTROL I Filed NOV. 2,- 1945 4 Sheets-Sheet 4 I f i 32 56 1- /8 /Z l7 FIG. I6

82 PIC-3.14

INVENTOR.

Patented Jan. 8, 1952 AIRCRAFT Boron BLADE AND .BLADEMFLAP V rrron. CONTROL- Edward A. Stalker, Bayouy, Mich; Application November 2, 1945, seminqrszeass 3,Cl a ims. (:o1.17p 1so.25i

' Myg inventi n relat s particularlyto, theflift n m nts i d-ii' ct lii air r ft; and their methods.

t p ra i .-v a a p It is an objeet or theinvention to uprovidea lifting rotor;which. can be; operated; at high 'forward speed and high values of theadvance ratio. a

Ano henobiectis; to p ov de a. means. of p portioninggth power available between the lift- P8; 9.1 9 the. m answi p oducing forward.

ther bj ct llpp ar. it m-the, descrindrawin s .and aims Lac empli h t e. aboveobi cts by th eans illustrated in the accompanying drawings in n ht-'- v Eig-ure -1 is a, diagrammaticmp. view. of a, rotor showing the relative wind. velocity distribution acros the rotor diameter for an; advanceratio essh ni y-i.

Fi ure 2 is .,a;b1ade section, along liner-2 of Fi u e-1;. a I

figure 3 is; a diagram. of the. lift variatig'm acrossrthe diameter or a. rotor whose advance: t t os s t anuni figured isadiagrammatic top viewof arotor shpwing the relative wind velocitydistribution across the. rotor diameter for an advance 'ratio greater than unity;

Figure 5 isa diagram of 'the lift variation across the-diameter ofa rotor-whose advance ratioisgreaterthan unit-y:

Figure 6 is a; front elevation of the helicopter;

- Figure is a-=- side elevation of the helicopter;

Figure isa side -elevation-- largely diagram maticon the: nacelle ofthehelicopter- -o- Fig- I iii-e6; I

' Figure- 9; is a diagram; of the variation of lift with orbital position 01 theblade for an advance ratio greaterthan-unity;

Figure 10 is a diagram -oi thevariation of; pitch-and flapangle with orbital -position-of the blade-for an advance ratio greater than unity; Figure 11 is a diagramillustrating'the orbital positions of thebladesfor use with Figure-'10;

Figure. 12 isa diagram of the type of Figure m tor air-advance ratio less: than unity; v

Eigurefl 1-32 is. a blade section alongz=linerl.3-.l3. 4 shown in relation to the. relative wind; vec mt-ofiadvance;

Figure 14 is a fragmentary vertical-,rsectionelone1' ne nfieure a:

suraifi. a-perspective view.- of, the ring. am-as tmb yn I Figure t: i a Imsr ntarrt p p an ewi.

hereto:

Fi ure 17 is a section along the line I 1-411 of Figure '16;- and Figure-18 isa section along the. line l8--l8 in au e 1 r It. is taught in contemporarywork .on the helicopter thati it, is essentially a slow-speed ma,- chine,,a nd thatits forward speed cannot exceed about 0.4 of the tip peripheral speed, that. is, an.

advanceratioof 0.4.

invention discloses a means of attaining advance ratios of large magnitudes. above. 1.0..

A; limiting conditionin the helicopter occurs.

when the speed of sound is reached on the advancing wing or blade tip since then the drag mounts seriously. To avoid this I operate the. rotor at. decreasing. tip peripheral. speeds as the forward speed is increased and always keep thev tip ;re1ativ,e wind speedbelow the sonic velocity. That is the sum of the translational speed and the tip vperipheral speed is always less than some speed, I then operate the rotor blades in such a manner to obtain lift from the inboard portion, oftbaretreating blade to make up for the lowcred rate of rotation.

Normally the inboard portion of the, retreating blade l givesa negative lift L because the relative windas shownin Figure 1 is reversed over this portion and the angle of attack a is negativeas shown in- Figure 2. The distributions. 2. and, 4 of lift along the spans of the retreating and. advancing blades respectively are shown inEigure v3.

In this invention the rotor is operated athigh. speed, with. the velocity distribution shown-fin Eigure l Therelative windvelocity at. the ad:- vancing blade A. is; less than. the velocity ofsound and the forward velocity is substantially higher than, the tip peripheral speed. In fact Figure; 4 itis 1 2.14 times. the tip peripheral, speedl Hence, .;theflowon the retreating blade R is from Whatis normally the trailing edge. (T. E.) to the, leading edge ,(L E.) along. thewhole radius. This results in a. lift distribution. along the, radiias shown .in'Figure 5.

Inhorder to achieve thev proper lifts on the blades to-:make-the rotor balance and have ,a.

ity has .valuesv corresponding to a straight line variationjjrom' tip to tip as indicated by line 6. At a point 8 the relative wind velocity is zero and inboard from this point the relative wind is reversed. That is, it flows from what is nor-' mally the trailing edge to the leading edge 'As already set forth this leads to a negative angle" 5 of attack and a negative lift forthe inboard portion of the retreating blade.

In Figure 4 the forward speed (Va) is so high that on both blades the relative wind is in the same direction, that is in. the direction'bpposite proaching the =270 position. The pitch is again decreased for the D4 position.

It will be noted that this pitch variation is different from what would be required for operation for an advance ratio less than 1.0. For the ratio below 1.0 the pitch angle of the blade in the positionR would be made a positive maximum and jthe pitch at Ds -a'nd D4 would be less than at R.

These pitch and flap variations may also be expressed in terms of the true angle of attack measuredbetween-the zero lift line of the section and the local relative wind vector found as aresultant of the advance and peripheral velocity vectors. Thus, due to the pitch variation in- Figure 10,-the angle of attack is positive on I the advancing side almost up to F :180).

to the flight direction of "the aircraft. As a'resuit the retreating blade under the special con ditions provided is made to carry a positiv'e'lift along its whole span outside the hub sides The lift of the advancing and retreating blades are: adjusted so thatthe total lift of the'rotor remains constant and equal to the weightof On thcreti-eating side the angle of attack is a positive maximum at D; and D4 and still positive at R but of less magnitude than'at Diand D4. Here it- 'must be remembered that the 'resultant relative wind is still rearwardbeoause' the advance ratio is greater than 1, and the zero lift line of the section points upwarjd andffor the machine for changing orbital positions of the blades.

In order not to encounter largedragsarising; 3 from: supersonic effects the value Of'Vp in Figure 4 is reduced belowthe value in Figure 1 and the;

sum of Va and Vp is keptbelow sonic speed by decreasing the rate of rotation as the aircraft;

speed] i have relaq.

The orbital variation of lift coefficient on the I bladefmu'st be different for an advance ratio greater than 1 (Figure 4) than for aratio less;

than 1 (Figure 1).

A proper variation in lift for the higher-advance ratio is shown in Figure 9 wherein it will be observed that the lift coefiicient CL attains two peak values near the D3 and D positions "as shown in Fig. 11. It is particularly significant that on the retreating side the lift coefiicient must be higher for the diagonal positions D: and D4 than for the most laterally extending posi-' tion R. The front and back positions (F and B) also have larger values than for theft position. V I Such a variation in lift can be attained by various combinations of pitch and flap angles;

Figure 10 shows a proper variation of the angle of pitch (curve M) and of the angle 5 for the flaps (curve It) to achieve the lift variation shown in Figure 9. The azimuth or orbital angle (psi) is measured from the rear blade pdsition as indicated in Figure 11 by =0. -'Me asuringfrom this position the blade (on the'a'dvancing side) increases its positive pitch angle up to approximately 0:90 then'decreases the angle until the front position F is reached at =180. The flap angle 5 may have other values than zero for the R and A positions but they are preferably of approximately equal value as shown in Fig. 10. On the retreating side the pitch is made negative so that the effective angle of attack is positive with respect to the resultant wind which attacks the trailing edge of the retreating win because the forward speed exceeds the peripheral speed. on this side the pitch is decreased greatly in approaching the diagonal position D3 and then increased in apward, that is toward the nose of the aircraft; It will be noted that the flap angle 5 is substan--' tially zero for positions R and A buthas airlaX- imum angle for both =0 and =180,-"that is the front and back positions F and B respectivelyi.

Both the pitch and flap angles have minimum magnitudes (but opposite signs) for'the retreating position R, when the advance ratio is greater than 1.0 while the reverse is true when-the ratio islessthan1.0.

The patterns of pitch and flap variation can'be changed since a change-in one can always b''overridden by a prope'r'change in the other. The fundamental variable, as remarked, is really thelift coefficient of the blade at some representative section along the span of the" blade. The lift coefficient follows .the pattern shown in Figure '9' and the combination of fiap and pitch variations of Figure 10 results in such a curve. It is charac-' terized by the peaks for the D3 and Dr positions" of the blades, rising. well above the lift coefficient at the retreating position R (270). .Thecurve,

shown is for approximately the, midpoint offthei radius of therotor. t

As remarked just above, a variation in flap Sea ting can offset a variation in pitch setting. This is true even for the flap-acting at the nose of the airfoil section. For instance, it will be clear from Fi re 3, at w rins h f a linen dest oy Va arising from the forward speed-which exceeds;

the tip'peripheral speed-,Vp.

:The true or .efliective angle ofgattack is-always tobe measuredwith respect ;to the zero lift line, (marked L=0) of the section as shown in Figure 13 and the local relative wind vector which istheresultant of the vectors due to forward speed and rotation and any other-effect'which may-be pres;- ent. This hero lift line is to befound by the wellknown method due to .Munk. It will be observed that lowering the flap decreases the angle of:

Theblades l and a and hub zo jeir'ipo lifting rotor"2 2. As shownparticularly-in'Figure 14, the blades are individually mounted"iri bear ings 24 for rotation with respect to the hub about a spanwise axis.

The pitch attitude of the blades is controlled by the cam assembly 30 (Figures 14 and 15) whose ring cam 3| is operably connected by links 32 to the arms 34 fixed to the shanks of the blades.

The flaps are controlled by another ring cam 50 similar to 3|. Link 52 is operably connected from the cam to the arm 54 fixed to the torque tube 56 in turn fixed to the inner end of the flap I2.

The configuration of the two-ring cams are related through slideable slotted plates 60. (See Figure 15 particularly.) Outer slots 62 and inner slots 64 are of appropriate shape to give ring cams 50 and 3| the correct contours for controlling the flap and pitch angles in coordination.

The plates 60 are slidable in the plate 65 by arms 66 fixed to ring 61 borne for vertical sliding on part 68. The pilot can adjust the position of ring 61 by turning rod 69 which is threaded through the ring. The vertical movement of the ring moves roller vertically and slides plate 60 horizontally.

Since plate 65 is universally mounted on the ball 12 it can be tilted by a suitable rod 14 and another spaced 90 degrees around from it, both articulated to the plate 65. Plate 65 and ball 12 may also be slid vertically on the tubular bearing 16 b means of rod 18.

Each helicopter rotor is turned by the engine 80 connected to the rotor shaft 82 by means of the variable speed drive 84 which can be operated by the pilot by means of control rod 86.

The engine also drives the variable pitch propeller [0 to provide a propulsive force perpendicular to the axis of shaft 82 (which is also the rotor axis of rotation). As the speed of forward flight increases less power is applied to the rotor 22 and more to the propellerl0. To decrease the power going to the rotor the variable speed transmission is operated to reduce the rate of rotation of the rotor. To absorb the power of the engine 80 the pitch of the propeller I0 is increased and its rate of rotation is increased by means of the variable speed transmission 88 actuated by the pilot by means of control rod 90.

The engine 80 and the propeller I 0 may be considered a power means whose power is in part applied to the rotor to rotate it while part is used in the propeller. As the speed of flight is increased progressively more power is expended through thethrust-producing propeller and less through the lift-producing rotor. This is possible since more and more lift arises from the forward speed.

The principal feature of this invention is the provision of means for operating a helicopter at an advance ratio greater than 1. To do so unique attitudes are given to both the advancing and retreating blades. For instance, the retreating blade is rotated in pitch in the most laterally extending position so that its outer portion has a positive angle of attack with respect to the relative wind vector due to the advance. In contemporary helicopters the positive angle of attack is with respect to the relative wind vector due to the rotation.

Furthermore, the pitch of the blade in the most laterally extending position is different from the pitch in the diagonal position on either side of the most lateral extending position. Thus the true angle of attack between the blade and the local relative wind is more positive for the diagonal positions than for the most laterally extending positions. The conventional helicopter (advance ratio less than 1) has the opposite order of magnitudes of angles of attack.

The invention also consists in providing suitable mechanical features to execute the variation in lift with orbital position and in providing for flight at low advance ratios in a machine capable of attaining high advance ratios.

I have now described suitable embodiments of my invention which are now preferred. It is to be understood however that the invention is not limited to the particular construction illustrated and described and that I intend to claim it broadly as indicated by the scope of the appended claims.

I claim:

1. In combination, in an aircraft, a blade sup ported for rotation about an upright axis and for pitch adjustment, said blade having an adjustable flap, means operable cyclically to adjust the pitch of said blade, additional means for cyclically adjusting the attitude of said flap rela tive to said blade separately from said pitch adjustment, and means for coordinating the operation of one of said adjusting means with the other.

2. In combination in a direct lift aircraft, a rotatable blade, means mounting said blade for rotation about an upright axis, means for adjusting the lift of said blade, a tiltable control plate, a deformable cam mounted on said plate,

means in running contact with said cam operably connected to said adjusting means to cyclically alter the blade lift in accordance with variations in said cam contour, means to deform said cam to alter the orbital lift pattern of said blade, and means to tilt said plate to displace said cam relative to said adjusting means to actuate said adjusting means to superimpose a lift change on the lift alteration induced on said blade by deforming said cam.

3. In combination in a direct lift aircraft, a rotatable blade, means supporting said blade for rotation about an upright axis, two separate means for adjusting the lift of said blade, a deformable cam for each of said adjusting means, means in running contact with each said cam operably interconnecting each said cam with its respective said adjusting means, means controlled by each said cam for causing orbital variations in blade lift in accordance with variations in the contour of its associated cam, and means to deform said cam contours in coordinated relation with each other.

EDWARD A. STALKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

